1. Field
The following description relates to exploration geophysics technology, and more particularly, to a technology which visualizes subsurface velocity structure through signal processing using waveform inversion.
2. Description of the Related Art
Waveform inversion is a technique which estimates a subsurface velocity model using pre-stack seismic data.
Waveform inversion is a process which, after creating an initial model for a target region and obtaining a measured data in the target region, iteratively updates the initial model using the measured data to obtain a subsurface velocity model that is similar to the true subsurface structure. The waveform inversion is performed by computing modeled values from an initial velocity model by computer, and iteratively updating parameters representing physical properties of the subsurface until errors between the modeled values and the measured data obtained through actual field exploration are minimized.
Waveform inversion, a method for velocity analysis to achieve the goals of geophysical exploration, includes various mathematical methods. A representative waveform inversion method is a least squares method. With the development of computer technology, simple inversion is solved by a personal computer, and in most cases, certain prior information is applied to obtain an optimal solution since cases of obtaining a unique solution seldom occur. Here, it is an option to assign more importance on minimizing the error between the measured and modeled data or on obtaining a solution that is close to the prior information. Since an inversion model requires extreme assumptions as well as simplification in many cases, information about the geological and physical properties of the earth's interior is commonly used when a waveform inversion is performed.
One of the most important geological and physical properties of the earth's interior to delineate the subsurface is seismic propagation velocity. For example, to obtain the seismic propagation velocity of the subsurface, research is currently being conducted into artificially generating a wave in a target region that is to be measured, measuring a seismic wave in the target region, and performing waveform inversion in the time or frequency domain for the measured seismic data.